Reference for Sheviit 3:9

אַבְנֵי כָתֵף, בָּאוֹת מִכָּל מָקוֹם. וְהַקַּבְּלָן, מֵבִיא מִכָּל מָקוֹם. וְאֵלּוּ הֵם אַבְנֵי כָתֵף, כָּל שֶׁאֵינָהּ יְכוֹלָה לְהִנָּטֵל בְּאַחַת יָד, דִּבְרֵי רַבִּי מֵאִיר. רַבִּי יוֹסֵי אוֹמֵר, אַבְנֵי כָתֵף כִּשְׁמָן, כָּל שֶׁהֵן נִטָּלוֹת שְׁתַּיִם שָׁלֹשׁ עַל הַכָּתֵף:

"Shoulder-stones" may be brought from any place. A contractor may bring [any type of stone] in from any place. "Shoulder-stones" are: any [stone] which cannot be picked up with one hand - thus says Rabbi Meir. Rabbi Yosi says, "shoulder-stones" are as they sound - any [stone] which can be carried two or three on one's shoulder.

Jastrow

Jastrow